Search

Alternating current electrophoretic deposition (AC–EPD) was used to infiltrate a SiC-based matrix phase containing Al 2 O 3 –Sc 2 O 3 sintering aids into the fine voids of a two-dimensionally woven Tyranno™-SA3 SiC fabric preform for the fabrication of a dense SiC fiber-reinforced SiC composite (SiC f /SiC). The zeta potential of the aqueous suspension was set to ≥−55 mV to achieve uniform and simultaneous deposition of all constituent particles. EPD was performed at 20 V AC for 30 min under the application of ultrasonic pulses for the initial 20 min to minimize the surface sealing effect. A high SiC f /SiC density of 96.5% along with a flexural strength of 413.9 ± 18.5 MPa was achieved after hot pressing at 1750 °C for 1 h due to the high degree of matrix phase infiltration. These results showed that an eco-friend AC–EPD process can be applied to the fabrication of high density SiC f /SiC. [ABSTRACT FROM AUTHOR]

Abstract: To explain the sintering behavior of 5wt.% Sc-nitrate-added SiC, which showed a 99.3% density with the fine 156nm-sized grains, a microstructural study using high resolution electron microscopy (HREM) was performed and the results were compared with those of Tm-added SiC, which had a mean grain size of 753nm. Contact flattening was proposed as a governing sintering mechanism for Sc-added SiC based on the experimental observations of an inter-granular phase thinner than 1nm along with the straight grain boundaries. On the other hand, the Tm-added SiC showed a several nm-thick inter-granular phase with a curved grain boundary morphology, which is the typical microstructure that can be obtained by a solution–reprecipitation mechanism combined with Ostwald ripening. [Copyright &y& Elsevier]

Abstract: Fourteen rare earth elements in their nitrate form were evaluated as sintering additives for β-SiC. All rare earth nitrates transformed to oxides by a reaction with the surface-adsorbed thin SiO2 during heat treatment, which enhanced the density of the SiC monolith without decomposing SiC. In particular, Sc, Yb, Tm, Er and Ho were quite effective sintering additives; a >99% relative density was observed by the addition of 5wt.% rare earth oxide, whereas the other rare earth additives (Lu, Dy, Tb, Gd, Eu, Sm, Nd, Ce and La) revealed 77–92% density. Moreover, a fine 156nm-sized SiC grain could be acquired by Sc addition, whereas the other additives showed a SiC grain size of approximately 1μm. The mean hardness and K Ic of the dense SiC containing rare earth elements were 24–27GPa and 3.3–5.0MPam1/2, respectively. [Copyright &y& Elsevier]